Investigating the Performance of IGS Real-Time Global Ionospheric Maps under Different Solar Conditions

Abstract

In recent years, real-time global ionospheric map (RT-GIM) products have been actively developed by the international global navigation satellite system (GNSS) service (IGS) and its ionosphere associate analysis centers (IAACs) along with the increase of RT-GNSS multi-frequency and multi-constellation observations. In this study, the accuracy and consistency of three RT-GIM products from the Chinese Academy of Sciences (CAS), Wuhan University (WHU), and IGS are evaluated and analyzed utilizing three validation methods, namely, comparison with JASON-3 vertical total electron content (VTEC), the difference of slant total electron content (dSTEC), and IGS combined final GIM (IGSG) data. The test period was from 1 January 2019 to 31 December 2022, including the different solar activities. First, the comparison with JASON-3 data illustrates that the quality of the three RT-GIM products over oceans is in great consistency with that of the IGSG during different levels of solar activity and the daily mean bias (MEAN) values in low and high solar activities are approximately 5 and 10 TECU, respectively. The root mean square (RMS) values under low and high solar activities can be up to 7 and 12 TECU. Furthermore, the dSTEC validation results present that the MEAN values of RT-GIM products from different IAACs at high- and mid-latitude stations are about 0.5 TECU, which is smaller than those at low-latitude stations at about 1 TECU over continental regions. The standard deviation (STD) and RMS values for various RT-GIM products are within 3 and 4 TECU at low latitudes, respectively. In terms of the comparison with IGSG, the result shows that IGS combined RT-GIM (IRTG) presents better consistency than CAS RT-GIM (CRTG) and WHU RT-GIM (WRTG) in 2021 and 2022, with average annual STD and RMS values of 2.56 and 2.78 TECU, respectively. The daily biases of the RT-GIM products relative to IGSG can reach 4 TECU in high solar activities and the daily STD and RMS values are mainly within the 5 to 6 TECU range, respectively.

Investigation of the Contribution of Five Broadcast Ionospheric Models (GPSK, NTCMG, NEQG, BDGIM, and BDSK) and IRTG to GNSS Positioning During Different Solar Activities in Solar Cycle 25

“…Since January 2021, a version of the IGS combined RT-GIM (IRTG) has been publicly and routinely generated based on the RT differential STEC weighting technique from different IAACs (N. Wang et al, 2022). Previous studies have shown that the accuracy of the IRTG is equivalent to the post-processed rapid GIM and higher than those of other IAACs (H. Liu et al, 2023;Q. Liu et al, 2021).…”

“…However, there is limited research on the performance evaluation of BDSK after 31 July 2021. Although several studies have evaluated the performance of RT‐GIM in the TEC domain (Li et al., 2020; H. Liu et al., 2023; Q. Liu et al., 2021; Ren et al., 2019), their assessment in the positioning domain, especially during high solar activity, is still limited.…”

“…However, there is limited research on the performance evaluation of BDSK after 31 July 2021. Although several studies have evaluated the performance of RT-GIM in the TEC domain(Li et al, 2020;H. Liu et al, 2023;Q.…”